A bipolar junction transistor (BJT) is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction between two regions of different charge concentrations. This mode of operation is contrasted with unipolar transistors, such as field-effect transistors, in which only one carrier type is involved in charge flow due to drift. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where they are minority carriers that diffuse toward the collector. For this reason, BJTs are classified as minority-carrier devices.
The BJT continues to be a valuable device in scaled technologies as designs converge to higher levels of system on chip (SOC) integration. As the technologies scale geometrically it becomes increasing important to provide high performance BJTs with minimum disruption to the main flow, which is further complicated by the addition of advanced technology elements like silicon on insulator (SOI) and high-K metal gates.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.